The present invention relates generally to field-type electron emitters, and, more particularly, to a system for addressing individual electron emitters in an emitter array. A field emitter unit includes a protection and focusing scheme that functions to minimize degradation of the electron beam and allow for focusing of the electron beam into a desired spot size. A control system is provided that allows for individual control of field emitter units in an array with a minimum amount of control channels.
Electron emissions in field-type electron emitter arrays are produced according to the Fowler-Nordheim theory relating the field emission current density of a clean metal surface to the electric field at the surface. Most field-type electron emitter arrays generally include an array of many field emitter devices. Emitter arrays can be micro- or nano-fabricated to contain tens of thousands of emitter devices on a single chip. Each emitter device, when properly driven, can emit a beam or current of electrons from the tip portion of the emitter device. Field emitter arrays have many applications, one of which is in field emitter displays, which can be implemented as a flat panel display. In addition, field emitter arrays may have applications as electron sources in microwave tubes, x-ray tubes, and other microelectronic devices.
The electron-emitting field emitter devices themselves may take a number of forms, such as a “Spindt”-type emitter. In operation, a control voltage is applied across a gating electrode and substrate to create a strong electric field and extract electrons from an emitter element placed on the substrate. Typically, the gate layer is common to all emitter devices of an emitter array and supplies the same control or emission voltage to the entire array. In some Spindt emitters, the control voltage may be about 100V. Other types of emitters may include refractory metal, carbide, diamond, or silicon tips or cones, silicon/carbon nanotubes, metallic nanowires, or carbon nanotubes.
When used as an electron source in an x-ray tube application, field emitter arrays create challenges regarding the addressability and activation of each field emitter. That is, in existing designs of field emitter arrays, each of the emitters in the array is addressed in turn via an associated bias or activation line and at appropriate time intervals. Due to the large number of emitter elements in a typical array, there can exist an equally large quantity of associated activation lines and connections. The large number of activation lines need to pass through the vacuum chamber of the x-ray tube to supply the emitter elements, thus there necessitates a large number of vacuum feedthroughs. There is an unavoidable leak rate associated with any feedthrough device, which can lead to gas pressure levels in the tube that can inhibit performance of the emitter elements and their ability to generate electrons.
Additionally, it may be desired for the field emitters in the array to be arranged in one of many varying orientations. That is, depending on the specific application, the field emitters may not always be arranged in a “matrix” type orientation (e.g., a 3×3 matrix/array of emitters), but may also be arranged in a linear array or in different patterns. Such patterns and arrangements can cause additional challenges with respect to the connection of each field emitter to an associated activation line and connection.
Thus, a need exists for a system for controlling the emitter elements in an emitter array that reduces the number of activation lines and feedthrough channels. It would also be desirable for such a system to be able to operate independent of the physical topology of the emitter elements in the emitter array.